Methane 'belch' theory gets boost By Julianna Kettlewell
Methane 'belch' theory gets boost
By Julianna Kettlewell
BBC News Online science staff
Scientists have found a series of vents in the Nordic Seas that may have
burped enough methane to cause massive global warming 55 million years
The early Eocene Period witnessed a dramatic increase in temperature,
which was triggered by a sudden surge of greenhouse gases in the
But just where these gases came from has been something of a mystery.
Nature magazine reports the discovery of gas vents dating from the right
time and which could represent the source.
At the beginning of the Eocene, the Earth's temperature suddenly shot up
five Celsius. It was one the most dramatic global warming events that has
been recorded in geologic history.
For human evolution, it was a vital period. The warm climate allowed
mammals to disperse across the Earth, diverging as they did so into many
groups. Among these newly emerging groups were mankind's primate
Scientists usually agree about the cause of this 100,000-year heatwave: a
pulse of carbon dioxide (CO2) hit the atmosphere to launch an extreme
However, what does cause a large amount of discussion within the
scientific community is just how this gas was produced.
One popular theory relates the existence of hydrates - a frozen mixture
of water and
methane produced by microbes - which are locked in ocean sediments. If
warmed up enough, the argument goes, then these hydrates would have
disgorging their load of methane.
The methane (a potent greenhouse gas itself) would have then broken down
to produce a CO2 surge. This process needs to be kick-started by minor
global warming, and some scientists suggest that the collision of a comet
or asteroid might have done the trick. But these accounts have suffered
from a lack of direct evidence.
Now a team of Norwegian scientists have hit upon something that could
creation of these greenhouse gases.
While studying charts of sedimentary rock produced by companies
petroleum, they noticed a series of hydrothermal vents.
They believe that trapped organic matter was heated so intensely by angry
seams of lava that it broke down into methane and forced its way to the
surface forming these
"We believe these hydrothermal vents are a likely explanation for the
gases that caused the climatic change," Bjorn Jamtveit, of the University
of Oslo, told BBC News Online.
However, the theory has been met with some scepticism. This is largely
because the carbon these vents belched would have been rich in a form -
or isotope - that does
not tally with geological records.
Rock deposits indicate the massive CO2 surge of 55 million years ago
lot of the isotope carbon-12. But the carbon produced when organic matter
intensely by lava contains a greater proportion of carbon-13.
"The problem is that the carbon released is the wrong sort of carbon,"
explained Mark Maslin, of University College London, UK. "I just don't
find it a plausible theory."
The only way this theory could explain the high levels of carbon-12 at
of the Eocene is if truly enormous amounts of gas were produced. That
though it contains proportionally less carbon-12, the carbon cycle is
"It is a bit like having a swimming pool filled with white paint,"
Dickens, of Rice University, Houston, US. "If you want to turn that
swimming pool pink, you can either add a little red paint or a lot of
In other words, the gas produced by hydrothermals represents pink paint.
To get the
effect recorded, you need an awful lot of it.
According to Professor Jamtveit, there was indeed an awful lot of it.
calculate the amount of gas that can be released by this process it is
said. "It corresponds to the amount of gas in the petroleum resources in
But Dr Maslin remains unconvinced: "I can't imagine that amount of carbon
released just through the Nordic Seas," he said.
If the hydrothermal vents did not cause the Eocene thermal maximum that
worrying news for us.
The vents only spewed methane because of a rare spate of laval activity.
happen again, but probably not in the near future.
On the other hand, if the hydrate-release theory is true; if minor global
cause gas hydrates in ocean sediments to melt and shed their methane
could be heading for trouble.
Dr Maslin put it bluntly: "We've got global warming occurring - and if we
keep it up
will all the gas hydrate be released to cause super global warming?
think the answer to that is 'yes'."
LINKS TO MORE SCIENCE/NATURE STORIES
Ocean Burps and Climate Change?
By Gavin Schmidt
About 55 million years ago an event known as the Paleocene-Eocene Thermal
Maximum (PETM) occurred. This was an episode of rapid and intense warming
(up to 7�C at high latitudes) which lasted less than 100,000 years (see
Figure 1). Curiously, the PETM was accompanied by an
change to the global carbon
cycle as indicated by a large drop in
the isotopic ratio of 13C to
12C in the ocean and on land.
The ratio of these carbon isotopes generally changes as a
of biological activity, since
carbon in living matter tends to be
preferentially made up of 12C
as opposed to 13C. Thus an
increase in biological activity
"uses up" more 12C, and therefore
the ratio of 13C to 12C in the
remaining carbon increases.
Conversely, a decrease of
biological uptake, leads to a decrease
of the isotopic ratio (i.e., it
The change at the PETM was so
large that it would have required
a decrease in biological
activity equivalent to roughly three times
the total present-day
terrestrial biosphere. In other words, if all of
the terrestrial carbon today
(in forests, animals, soils, etc.) were
converted to carbon dioxide and
returned to the global inorganic
carbon pool, the change in the
global carbon isotopic ratio would
only be a third as big as that observed during the PETM! However,
no such event is seen at the
PETM, and thus another source for
very "light" carbon must be
Volcanos are another source of light carbon as carbon dioxide gas
within eruptions. But this
source would also imply an enormous,
and highly unlikely, amount of
volcanism to match the
observations. In fact, only one source of carbon that is isotopically
light and available in large enough quantities has been pinpointed
so far, this is the reservoir of methane hydrate deposits (Figure 2)
buried on the continental
shelves of the oceans (Figure 3).
Bacteria produce methane as
they decompose organic matter in
the ocean sediments, and in
cold, high-pressure environments,
methane hydrates will form.
This is an ice-like solid that consists
of methane surrounded by water
molecules in a lattice structure.
However, if the temperature
warms, or the pressure is reduced
(for instance if local sea level decreases), the hydrate will break
and release the methane as gas which can bubble up through the
ocean and enter the atmosphere.
What would be the consequences
of such a large emission of
methane into the atmosphere? At
present, methane has a
residence time of about 10
years before it is oxidized to carbon
dioxide. However, the chemistry
of this process is highly
non-linear, and as emissions
increase, the capacity of the
atmosphere to deal with the
excess methane decreases and the
residence time lengthens. This can lead to quite large increases in
the methane concentration. This
matters because molecule for
molecule, methane is a more
powerful greenhouse gas than
carbon dioxide. The climate
consequences depend very strongly
on exactly how long the extra
methane hangs around.
Our research (described in
Schmidt and Shindell 2003) has
examined these chemical and radiative effects. Based on
scenarios for what may have
occurred at the PETM, we tried to
estimate the history of the
methane and carbon dioxide
concentrations. Using radiation modeling we estimated how strong
the climate forcing would be
for each scenario, and then ran
general circulation models to
see how that forcing would change
We found that for some
scenarios, the methane levels can stay
high enough and remain long enough to play the dominant role in
the subsequent climate warming.
The temperature changes are
close enough to those observed through the PETM to support both
the hypothesized scenario and
our modelling efforts. While there
are huge uncertainties in
almost every aspect of this study, this
research shows that we can
"connect the dots" from a methane
hydrate forcing to the observed
Methane plays a large role in
present day climate forcing (see
"Trends of Measured Climate
Forcing Agents" for more details)
and has more than doubled in
concentration since the
pre-industrial period. This study goes a long way in
role in paleoclimate
variability as well.
Schmidt, G.A., and D.T.
Shindell 2003. Atmospheric
forcing, and climate change as a
consequence of a massive
methane release from gas
Paleoceanography 18, 1004,
Please address all inquiries about this research to Dr. Gavin
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